(1) Field of the Invention
This invention relates to catheters made of plastic material for gaining temporary vascular access to the circulatory system of a patient requiring hemodialysis.
More specifically, such a catheter is designed to catheterize a predetermined blood vessel of a patient by a single puncture. The catheter is inserted into the blood vessel so that untreated blood is withdrawn continuously from that vessel and passed to a dialysis apparatus. Processed blood is returned from the apparatus to the same blood vessel.
(2) Description of the Prior Art
It is well accepted medical practice in the performance of both emergency and chronic hemodialysis to use a double lumen catheter of concentrically disposed tubular construction. See, for example, FIG. 5 in Raulerson, U.S. Pat. No. 4,037,599, and FIGS. 3, 4 and 5 in Allentyne Limited, Canadian Pat. No. 1,092,927.
The placement of catheters of this type is accomplished commonly by the "Seldinger" technique. This technique involves the puncture of a vein with a hollow needle. A flexible stainless steel wire is then threaded through the needle and into the vein. The needle is withdrawn over the wire and the flexible plastic catheter slipped down over the wire, as a guide for proper placement of the distal end of the catheter inside the blood vessel. A typical subclavian application of a double lumen catheter is shown in Canadian Pat. No. 1,092,927.
It can be seen that once the catheter is inserted into the vein of a patient, it serves as a linkage between the blood stream and an extracorporeal hemodialysis circuit. The arterial lumen of the catheter captures, from the vein, the arterial blood to be treated and the venous lumen returns fresh or processed blood (venous flow) into the same vein downstream of the blood flow. This arrangement makes the extracorporeal hemodialysis circuit, including the catheter, in effect, an extension of the patient's vein.
There must be an opening at the distal tip of the catheter large enough to receive a guidewire. The surface surrounding this opening must be rounded and smooth and the diameter of the body of the catheter must increase gradually and smoothly to ease its insertion.
Even though dialysis may only be performed intermittently, it is common to leave the catheter in the patient's vein for some time, say up to about two weeks, and between dialysis to inject into the catheter a drug to prevent blood clotting, for instance heparin. It is desirable that the drug remain in the catheter for as long as possible.
A major problem in catheterizing is kinking of the catheter during insertion. One attempt to overcome this has been to employ, in the outer tube of a concentric double lumen catheter, relatively heavy tubing, for example, of Teflon, and to rely on the wall thickness to prevent kinking. While the thicker tubing impedes insertion, it has not been altogether effective to prevent kinking and a proportion of catheters made in this way still kink.
Another problem with the concentric tubular construction is that, despite the size of the tubing, the lumen does not allow adequate blood flow, because of the significant thickness of the wall compared to the overall diameter and the significant cross-sectional area of the inner tubing.
A still further problem is that there is dead space in the Y-adapter commonly forming a part of the catheter causing disorder of the blood flow. Blood clotting also takes place more frequently with double lumen catheters than with single lumen catheters.
An aim of the present invention is to provide catheters and methods of making them which overcome these problems and which provide positive advantages as will be apparent from the detailed description to follow.